A successful project in Bethnal Green


Recently one of our experienced energy assessors, Jordan Howlett, was able to help a client find a better solution to meet their Code for Sustainable Homes requirement while keeping their costs down.

The project comprised 67 new flats and maisonettes within an apartment complex in Bethnal Green, London. The requirement was to achieve Code Level 4 and a challenging 20% reduction in CO₂ emissions through the use of renewables.

Jordan completed the SAP calculations and worked closely with the client to ensure that the dwellings achieved enough credits under the Code, and enough of a reduction in CO₂ to satisfy the planners: no easy feat! Once the targets had been achieved, he was able to advise on how their strategy could be improved to ensure compliance whilst keeping costs down. As an example, he proposed a strategy for the external water collection that was both compliant with the Code and efficient in terms of cost, space and installation.

After submitting this assessment, the client received their CSH certification within two working days. They were extremely pleased with the service we provided, and we felt the best possible sustainability solution had been found, to the advantage of the client, the new home-owners and the environment.

If you’d like to know more about our tailor-made assessment services, contact us on 01454 317940 or email at enquiries@darren-evans.co.uk. We’d love to help.


Thermal bridging: a primer and an update

Hopefully you are all aware that the details for thermal bridging using aircrete blocks have been updated and are now available. Partial fill cavity wall details were updated just eight days ago. If not, read on!

What is Thermal Bridging?

Thermal bridges occur at junctions: for instance, where walls meet, where a wall meets a floor, or where a wall meets a roof, window or door. Generally speaking, they occur in a building where a material with poor insulating properties passes through an insulation system, causing a ‘bridge’ for heat to escape. There are two main types of thermal bridge. A repeated thermal bridge, such as the studs in a timber frame wall, is dealt with in a conventional U-value calculation. A non-repeated thermal bridge occurs, for example, around openings, using a section of steel in a timber frame wall, or the junction between different elements types, such as a wall and a floor.

It’s worth noting that it is important to get your assessor to calculate the junctions rather than putting in the default value: this can have a big effect on the overall build costs and whether you choose full fill cavity wall insulation or partial fill. For a recent, real-world example, please see our engagement with Celotex and Cumbrian Homes, here.

What is a ψ-Value?

The heat loss associated with the non-repeated thermal bridge is called linear thermal transmittance, or psi-value or ψ-value (pronounced ‘si’). This is the rate of heat flow per degree per unit length of the thermal bridge that is not accounted for in the U-value of the plain elements. This is illustrated below where the heat loss path is indicated by the arrows. The larger arrow in diagram (a) indicates a greater heat loss.

The concept of a ψ-Value

Repeated thermal bridges such as timber studs or mortar joints are already covered by U-value calculations, but it is the heat loss at junctions between the various building elements that will be addressed by Constructive Details.

This extra heat loss, which is over and above the heat flow through the adjoining plane elements in a junction, is the linear thermal transmittance or ψ-value expressed in W/mK. To calculate this value one needs to subtract the heat flow through the plane elements (expressed by the U-value multiplied by the length of the element) from the total heat flow from the external to internal. This principle is illustrated in the drawing of the wall–floor junction. The image alongside showing the temperature distribution for the same junction is taken directly from thermal modelling software.

thermal bridging

The evaluation of thermal performance of both elements and whole constructions is becoming increasingly important. Another factor that is becoming increasingly significant is linear thermal bridging and the need for accurate and reliable calculations.

How can I calculate a ψ-Value and what are the relevant standards?

This is done with the use of computer programmes. All these programmes are adequate in estimating the heat flow through different types of junctions, in both simple (2D) and the more complex (3D) cases. The current acceptable methodology for calculations is the one described in BR 497 : 2007 Conventions for calculating linear thermal transmittance and temperature factors, and the documents Information Paper IP 1/06: Assessing the effects of thermal bridging at junctions and around openings and BS EN ISO 10211 Thermal bridges in building construction- Heat flows and surface temperatures-Detailed calculations.

Alternatively, if you are building with a lightweight internal skin of block (aircrete block), ψ-values can be sourced from the latest release from http://www.constructivedetails.co.uk. A set of ψ-values has been calculated for various common junctions for partial-fill and full-fill cavity walls. If you adhere to the requirements outlined in the documents, these enhanced ψ-values can be incorporated into SAP calculations. These values follow the same principle as accredited construction details; however, they consider more variables and are subsequently more accurate.

Why is it becoming important now?

The Approved Documents L1A and L2A (sections 5.12a and 5.7a) addressed the issues of thermal bridging, introducing the concept of a scheme for quality assurance of thermal bridging details. The context of this scheme is yet to be determined and in the meantime designers, energy assessors and specifiers tend to depend on the default values of the existing accredited construction details. These are potentially higher and less accurate than those that can be achieved by performing bespoke calculations, and they don’t cover all types of construction. Consequently, the heat loss estimated in a SAP calculation in such cases may be higher than expected based on the details used. As an alternative to using default values, individually calculated psi values can be used, but building control officers still need to satisfy themselves that the psi-values used have been created by a person with suitable expertise and experience. These values can be included within the BBA Certificate rather than having to rely on less accurate default values. Clients own existing values can also be accommodated following validation of the work. We can advise on individual client requirements for elements such as roof windows, roof lights, conservatory roofs, or even PassivHaus.

If you have any queries or projects that need quotes for any of Part L, please feel free to send them to Claire Beard at claire@darren-evans.co.uk, or call her on 01454 317940 .

Our thermal modelling service brings Celotex a satisfied customer


Recently Celotex Insulation Services, with whom we share a fruitful partnership, contacted us for help with a client. Cumbrian Homes were using full cavity wall insulation in their properties, which fulfilled their U-value requirements but was an expensive solution. We called in our Energy Assessor, Jordan Howlett, who modelled the properties. He calculated that the same U-values could be achieved with only partially filled insulation in the walls and roof.

Cumbrian Homes were able to spend less on insulation and save a great deal of money in construction. They were delighted with the service we provided, and Celotex were able to secure their business.

We’ll always try our best not only to assess your property but to work out the best possible deal for you. We know profit margins are tight, and we’ll do everything we can to save you money, while still providing the very best in sustainability solutions.

The Green Deal for customers: what do you need to know?


You may have heard that the Green Deal is now up and running. We hope you’re as excited as we are about its potential to transform properties and energy bills.

Let’s talk about the details: if you’re interested in using a Green Deal package for your own home, what is it you need to know?

What is the Green Deal?

You can read more about the details of the scheme in our Green Deal FAQ blog post, here. Essentially, Green Deal Advisors identify areas in your home where energy efficiency improvements, if made, would reduce the cost of your energy bills. The improvements are carried out by Green Deal Installers, your energy usage decreases, and you agree for your energy bill to remain the same until the cost of the installation has been recouped.

There’s also an option for you to pledge money of your own, if you want improvements that don’t fit within Green Deal parameters.

Is the Green Deal for me?

The Green Deal works when the improvements needed would significantly reduce your energy bills. Extra double glazing (in an already well-insulated and heated property), for example, is unlikely to save enough energy on its own to qualify for a Green Deal package.

Your house is an ideal candidate if it requires any of the following: new boilers, external/internal insulation, cavity wall insulation, or heating controls. These improvements would significantly improve the energy efficiency of your home and, once the cost of the installation is offset, you’d feel the benefit of lower energy bills for years to come. Solar, thermal or PV panels may sometimes fit in a Green Deal package, but not always. If you live in an area of fuel poverty, or are retired, you’re almost certain to get access to Green Deal finance. If you’re unsure, the best thing to do is ask us!

Why choose us?

Darren Evans Assessments is a certified Green Deal Organisation, which means we can organise a Green Deal Assessor to visit your home and begin the Green Deal process. Once the assessments have been completed, we’ll guide you through the results.

Unlike other, larger Green Deal Organisations, we have no affiliation to a particular Green Deal Provider, and have no provider services to sell ourselves. Our assessment fee is a flat £150, after which you’ll be free to take the results wherever you like. We’ll offer free, independent advice to help you choose the best provider for your needs.

And we know our stuff. We’ve worked in the energy and sustainability market very successfully since 2007, and tailor our service for some of the largest companies in the world as well as individuals who just want to make their property more comfortable. We were one of the first three companies to become accredited with the Green Deal, and we’ll use that experience to your advantage.

Our dedicated, competent assessors cover the whole of the UK: we have many assessors in the field and have the option of contacting 200 more, currently in training, if needed. So wherever you are, email greendeal@darren-evans.co.uk, or call us on 01454 317940 to find out more.

Your energy bills don’t have to be crippling. The Green Deal can help. Let us show you how. 

Green Deal Assessors: we need you!


The Green Deal is now up and running! As a certified Green Deal Organisation, we’ve had an amazing response from enthusiastic customers: around 2000 requests for Green Deal Assessments have poured in over the past few weeks.

And now we just need…you!

Would you like to work as a Green Deal Assessor under our banner? We’re passionate about offering better energy efficiency services to customers, and we’re keen to expand our team with likeminded partners. Here are just a few of the benefits we offer our team of dedicated associates:

Low registration fee

In order to lodge Green Deal Assessments, you’ll need to be registered with a Green Deal Organisation. Most companies are charging around £250 to £300 per year to be registered with their organisation. You can lodge your assessments with us for a one-off fee of only £25, even if you’re already registered elsewhere.

If you prefer, you can even wait until you’ve received an offer of work from us before you commit.

Free advertising

At the moment, Green Deal Assessors can only be found if their affiliated Green Deal Organisation promotes their services. We’ll make sure you have an online presence via our website and extensive social media services, and give you free access to our marketing material: we want you to receive as much work as you’d like to take on, and we’ll do everything we can to promote you.

Generous commission

We’ll agree your fees on a per-assessment basis, and if the customer decides to go ahead with Green Deal home improvements, you can receive an additional 1.5% commission on the cost of the work being done.

For example, if a customer decided on a package of work that costs £7000, we’d pass on an extra £105 to you, on top of your regular assessment fee. This applies to assessments we source for you and those you may have found yourself.

Full training

We’ll provide full technical training so you’re familiar with building legislation, the Green Deal processes and housing inspections, as well as wider training on business management and entrepreneurship. We want to further your career and help you expand your own skills as much as we can.

We’d prefer our Green Deal Assessors to be accredited with Elmshurst and to use e-Tech software. We can offer software training if needed, and if necessary we can also consider providing the equipment you’ll use as an assessor (an iPad or similar).

A welcoming business environment

We’re a dynamic, successful company with little formal hierarchy: if you have concerns or ideas that you’d like to be addressed by a director, we can put you through to the people at the top. We believe in adapting to our associates’ needs, and we’ll be determined to take care of yours.

Come and join us!

We have assessments now awaiting completion in Chelmsford and the London area; Bristol and Bath (including Taunton, Trowbridge and Weston-super-Mare); and Worcester and Birmingham. We’d love you to get involved.

For more information, please do contact us at greendeal@darren-evans.co.uk, or call us now on 01454 317940.